Overview of novel magnetically geared machines with partitioned stators

This study overviews recent development of a new class of magnetically geared machine topologies, i.e. partitioned stator (PS) machines. They are developed from magnetic gears and magnetically geared machines, as well as stator permanent magnet (PM) machines (switched flux, flux reversal, and doubly saliency PM), wound field, or hybrid PM and field winding machines. Based on the operating principle, i.e. magnetic gearing effect/air-gap field modulation and flux switching by the salient rotor iron poles, various PS machine topologies are developed. All have features of two stators, two air-gaps, and one segmented ferromagnetic rotor identical to a magnetic gear's modulating rotor. Their inherent relationships are revealed, while their electromagnetic performance is compared. Both PM and wound field PS machines are discussed, together with hybrid excited PS-PM machines and Vernier machines. It shows that all of these PS machines share the same torque production principle and the differences are mainly in PM configurations and relative positions of two stators. All PS machines have higher torque density per copper loss compared with their counterparts of single-stator machines. PS switched flux PM machines can produce the highest torque density per copper loss

Comparative study of partitioned stator memory machines with series and parallel hybrid PM configurations

In this paper, the partitioned stator (PS) structure is extended to variable-flux memory machines, forming two newly emerged PS switched-flux memory machines (PS-SFMMs) with series and parallel hybrid magnet configurations. From the perspective of geometry, both two PS-SFMMs share identical outer stator and rotor segments, while two different types of permanent magnet (PM) arrangements are employed in the inner stationary part. Thus, the developed machines can inherent the geometric separation of the armature winding and PM excitations from the PS design, thus achieving acceptable torque capability, and excellent air-gap flux control. A comparative study between PS-SFMMs with series and parallel structures is established. First, the topologies and operating principle are introduced, respectively. In addition, the design tradeoffs and PM sizing of the two PS machines are revealed and optimized with a simplified magnetic circuit model. Then, the electromagnetic characteristics of PS-SFMMs with different magnetic circuits are investigated and compared with the finite-element (FE) method. The FE results are validated by the experiments on a parallel prototype

Investigation of Doubly Salient Stator Slot Permanent Magnet Machines

Variable flux reluctance machines (VFRMs), which have both field and armature windings on the stator, are novel types of magnetless machines with a simple and robust mechanical structure and a low manufacturing cost. However, their electromagnetic performance, especially their overloading capability, is limited by high magnetic saturation due to field excitation. Therefore, circumferentially magnetized permanent magnets (PMs) are placed in the stator slot openings in order to (a) alleviate the magnetic saturation and (b) increase the torque capability based on VFRM, which leads to novel machine topologies, i.e. hybrid excited stator slot PM machines (HESSPMs) and stator slot PM machines (SSPMs). The effects of PMs in the stator slot openings are comparatively investigated for VFRMs, HESSPMs and SSPMs together with the discussion of the unique fault tolerant feature in stator slot PM machines. Furthermore, the overlapping winding (OW) layouts with coil pitches of 3 stator slot pitches are proposed in the three machine topologies in order to enhance the torque density. The electromagnetic performance of each machine topology, with OW and non-overlapping winding (NOW) and various feasible stator slot/rotor pole number combinations, is comparatively studied by finite element method. It shows that the proposed OW layout can improve the average torque of VFRM, HESSPM and SSPM with the optimal stator/rotor pole number combination. The proposed OW layout will be more competitive for the machines with a longer axial length and reduced end-effect. Prototype machines for these three machine topologies with both NOW and OW are built and tested to validate the finite element predicted results

Investigation of Magnetically Geared Stator Permanent Magnet Machines

Stator-permanent magnet (PM) (Stator-PM) machines include doubly salient PM, flux reversal PM (FRPM), and switched flux PM (SFPM) machines, in which both the PMs and armature windings are placed in the stator, whilst there is neither PM nor coil in the rotor. They have been the subject of much interest over the last 20 years. The operation and interaction mechanisms between the open-circuit and armature excitation magnetomotive forces (MMFs) in stator-PM machines have not been well described, however, which will be explained by the magnetic gearing effect in the first part of this thesis. It is found that similar to magnetic gears and magnetically geared (MG) machines, conventional single-stator-PM machines operate based on the modulation effect of the rotor to the open-circuit and armature excitation MMFs. It is also found that more than 95% of the average electromagnetic torque in SFPM machines is contributed by several dominant open-circuit and armature excitation air-gap field harmonics. The magnetic gearing effect in the partitioned stator SFPM (PS-SFPM) machines, which was proposed recently based on the magnetic gearing effect in the conventional single stator SFPM machines, is also investigated in this thesis. The partitioned-stator-PM machines also operate based on the magnetic gearing effect. Furthermore, over 93% of the electromagnetic torque generated in both the outer and inner air-gaps in the PS-SFPM machines is contributed by the dominant air-gap field harmonics. Consequent-pole PM topology and overlapping armature winding topology for the partitioned stator FRPM (PS-FRPM) machines, based on the magnetic gearing effect in the partitioned-stator-PM machines, are investigated in this thesis. By applying consequent-pole PM topology, about a third of the PM volume can be saved, but the torque density and efficiency are similar. For the overlapping armature winding topology, higher torque density, smaller loss, and hence larger efficiency etc. can be achieved when the machine stack length is relatively long. Finally, the PS-FRPM machines and the conventional MG machines, both of which have surface-mounted PMs, are compared in terms of electromagnetic performance. Compared with conventional MG machines, PS-FRPM machines have a smaller flux-leakage and hence a higher torque density and a larger power factor due to their smaller PM pole-pair number and iron piece number

Assisted Switched Reluctance Machines

Switched reluctance machine (SRM) modifications in both control schemes and physical design have been steadily increasing in academia to improve machine performance. Assisted switched reluctance machines (ASRMs) are a type of design modification for SRMs. Permanent magnets (PMs) and electromagnetic DC coils (DCC) are being added to the SRM to improve its torque output and overall efficiency. The choice for the design modification has been evolving throughout the decades. The focus has shifted from adding DCC to ASRM to adding PMs to ASRMs. This paper reviews the research trends of ASRMs and includes an analysis of the modified stator yoke design. Although adding PMs limit the application of machines away from extreme environmental conditions due to risk of demagnetization and increase material costs, the torque density and torque ripple reductions can out-perform DCC. PM ASRM are a good choice for energy efficiency-sensitive applications, but DCC, with proper control circuitry, can have a wider application and smaller initial build cost

Linear Machines for Long Stroke Applications: a review

This document reviews the current state of the art in the linear machine technology. First,the recent advancements in linear induction, switched reluctance and permanent magnet machines arepresented. The ladder slit secondary configuration is identified as an interesting configuration for linearinduction machines. In the case of switched reluctance machines, the mutually-coupled configuration hasbeen found to equate the thrust capability of conventional permanent magnet machines. The capabilities ofthe so called linear primary permanent magnet, viz. switched-flux, flux-reversal, doubly-salient and verniermachines are presented afterwards. A guide of different options to enhance several characteristics of linearmachines is also listed. A qualitative comparison of the capabilities of linear primary permanent magnetmachines is given later, where linear vernier and switched-flux machines are identified as the most interestingconfigurations for long stroke applications. In order to demonstrate the validity of the presented comparison,three machines are selected from the literature, and their capabilities are compared under the same conditionsto a conventional linear permanent magnet machine. It is found that the flux-reversal machines suffer froma very poor power factor, whereas the thrust capability of both vernier and switched-flux machines isconfirmed. However, the overload capability of these machines is found to be substantially lower than theone from the conventional machine. Finally, some different research topics are identified and suggested foreach type of machine

Design and analysis of novel asymmetric-stator-pole flux reversal PM machine

This paper proposes a novel flux reversal permanent magnet (FRPM) machine with asymmetric-stator-pole (ASP) configuration. Different from the conventional FRPM machine with uniform “NS-NS-NS” PM sequence, the proposed ASP-FRPM machine is characterized by a “NSN-S-NSN” magnet arrangement. Hence, the interpolar flux leakage is significantly reduced with the developed design, which can improve the torque capability. The machine topologies, features and operating principle are introduced, respectively. A simplified magnetic circuit model is established to reveal the underlying flux leakage reduction mechanism of the ASP design, and the rotor pole number is analytically optimized as well. The design parameters are then globally optimized so as to improve the torque quality. In addition, the electromagnetic characteristics of the ASP- and conventional FRPM machines are compared. Finally, experiments have been carried out to validate the theoretical results